Snow falls in front of the U.S. Capitol building on Feb. 13. / Mark Wilson, Getty Images

by Yamiche Alcindor and William M. Welch, USA TODAY

by Yamiche Alcindor and William M. Welch, USA TODAY

A massive storm blamed for at least 21 deaths paralyzed much of the East Coast with snow, sleet and ice Thursday, the latest punch from a tough winter that has left 49 of the nation's 50 states with snow on the ground.

As the South tried to dig out from a crusty layer of frozen snow and hundreds of thousands of people waited for the return of electric power, winter-weary New Yorkers were coping with a foot of fresh snow and much of the Northeast was bracing for more.

"I think we're actually seeing a little more snow than we expected - and we expected a lot of snow,'' said National Weather Service meteorologist Brian Korty.

Air travel was a disaster. More than 7,700 scheduled commercial flights were canceled across the USA, according to FlightStats.com, which tracks air travel.

Authorities blamed at least 21 deaths on the weather, among them two people who died after being struck by snowplows: A pregnant woman in Brooklyn who was loading groceries into her car when hit, and a snowplow driver who was struck by another state truck in Virginia. Min Lin's baby boy was in critical condition after being delivered nearly full term by cesarean section. No charges were brought against the snow plow operator and the tragedy appeared to be accidental, police said.

The ice and snow knocked out power across a wide swath. About 550,000 electricity customers remained in the dark, mostly in South Carolina and Georgia.

New York's new mayor, Bill de Blasio, drew criticism for his decision to keep city schools open in such difficult conditions. He countered with a simple tweet: "Since 1978 we've only had 11 snow days in New York City Public Schools."

Claire Zeng, 24, a business analyst who moved to the United States from Changsha, China, said she was weary of the arduous winter.

"If this continues, I will consider to move out," said Zeng, who is in her third New York winter. "It has been continuously snowing."

The storm is just the latest in a series of wintry blasts across much of the eastern half of the nation. Snow is now on the ground in 49 out of the 50 states, according to the National Oceanic and Atmospheric Administration. Only Florida is completely snow free, while Hawaii has snow near its volcanic peaks. But there is very little snow on the ground in usually snowy parts of Nevada, Arizona and New Mexico.

Snow totals varied widely. New York's Central Park was blanketed in 9.5 inches. Some areas around Washington, Baltimore and Philadelphia were reporting 7-10 inches, while the snowfall approached two feet in parts of Virginia and Maryland. Oakland, Md., saw 23 inches.

More is on the way.

Heavy snow will continue overnight in the Northeast, but will begin to taper off from south to north through the morning hours on Friday, according to National Weather Service meteorologist Allison Monarski.

An additional 12 to 18 inches, with locally higher amounts, can be expected through New England before the storm finally moves away Friday night.

Warmer air streaming in off the Atlantic should keep most of the precipitation as rain for coastal New England, with some mixing in of sleet or freezing rain possible.

Another storm will lead to some wintry precipitation in portions of the northern Plains and Mid-Mississippi Valley on Friday morning, which will spread into the Ohio Valley and Mid-Atlantic states by Friday evening and into New England on Saturday, the weather service predicts.

The storm could strengthen rapidly near Cape Cod, Mass., and could bring near-blizzard conditions to part of southeastern New England on Saturday, according to AccuWeather meteorologist Alex Sosnowski.

A change to warmer weather is possible beginning Monday and Tuesday across much of the country, and may continue through much of the rest of the month, AccuWeather is forecasting.

The massive flight cancellations and delays came after 4,000 flights were scrubbed Wednesday. Even warm, distant airports in Florida and California saw hundreds of cancellations because of the East's weather woes.

In Philadelphia, taxi driver Jeff Heaton, 57, said the heavy snow convinced him to organize his apartment Thursday. It's only the second day he hasn't worked in 2014.

"It slows everything down a lot," he said of the snow, adding that "a lot of people just don't come out."

The South took its biggest hit Wednesday and in the predawn hours of Thursday, and much of it was ice. In North Carolina, the storm caused huge traffic jams in the Raleigh area Wednesday as people left work and rushed to get home in the middle of the day.